Temperate earth-sized worlds found in extraordinarily rich planetary system (Update)

This artist's impression shows the view from the surface of one of the planets in the TRAPPIST-1 system. At least seven planets orbit this ultra cool dwarf star 40 light-years from Earth and they are all roughly the same size as the Earth. They are at the right distances from their star for liquid water to exist on the surfaces of several of them. Credit: ESO/M. Kornmesser

Astronomers have found a system of seven Earth-sized planets just 40 light-years away. They were detected as they passed in front of their parent star, the dwarf star TRAPPIST-1. Three of them lie in the habitable zone and could harbour water, increasing the possibility that the system could play host to life. It has both the largest number of Earth-sized planets yet found and the largest number of worlds that could support liquid water.

Astronomers using the TRAPPIST-South telescope at ESO's La Silla Observatory, the Very Large Telescope (VLT) at Paranal and the NASA Spitzer Space Telescope, as well as other telescopes around the world, have now confirmed the existence of at least seven small planets orbiting the cool red dwarf star TRAPPIST-1. All the planets, labelled TRAPPIST-1b, c, d, e, f, g and h in order of increasing distance from their parent star, have sizes similar to Earth.

Dips in the star's light output caused by each of the seven planets passing in front of it (astronomy)—events known as transits—allowed the astronomers to infer information about their sizes, compositions and orbits. They found that at least the inner six planets are comparable in both size and temperature to the Earth.

Lead author Michaël Gillon of the STAR Institute at the University of Liège in Belgium is delighted by the findings: "This is an amazing planetary system—not only because we have found so many planets, but because they are all surprisingly similar in size to the Earth!"

This artist's concept shows what the TRAPPIST-1 planetary system may look like, based on available data about the planets’ diameters, masses and distances from the host star. Credit: NASA-JPL/Caltech

With just 8% the mass of the Sun, TRAPPIST-1 is very small in stellar terms—only marginally bigger than the planet Jupiter—and though nearby in the constellation Aquarius (constellation) ) (The Water Carrier), it appears very dim. Astronomers expected that such dwarf stars might host many Earth-sized planets in tight orbits, making them promising targets in the hunt for extraterrestrial life, but TRAPPIST-1 is the first such system to be found.

Co-author Amaury Triaud expands: "The energy output from dwarf stars like TRAPPIST-1 is much weaker than that of our Sun. Planets would need to be in far closer orbits than we see in the Solar System if there is to be surface water. Fortunately, it seems that this kind of compact configuration is just what we see around TRAPPIST-1!"

The team determined that all the planets in the system are similar in size to Earth and Venus in the Solar System, or slightly smaller. The density measurements suggest that at least the innermost six are probably rocky in composition.

Imagine standing on the surface of the exoplanet TRAPPIST-1f. This artist's concept is one interpretation of what it could look like. Credit: NASA/JPL-Caltech

The planetary orbits are not much larger than that of Jupiter's Galilean moon system, and much smaller than the orbit of Mercury in the Solar System. However, TRAPPIST-1's small size and low temperature mean that the energy input to its planets is similar to that received by the inner planets in our Solar System; TRAPPIST-1c, d and f receive similar amounts of energy to Venus, Earth and Mars, respectively.

All seven planets discovered in the system could potentially have liquid water on their surfaces, though their orbital distances make some of them more likely candidates than others. Climate models suggest the innermost planets, TRAPPIST-1b, c and d, are probably too hot to support liquid water, except maybe on a small fraction of their surfaces. The orbital distance of the system's outermost planet, TRAPPIST-1h, is unconfirmed, though it is likely to be too distant and cold to harbour liquid water—assuming no alternative heating processes are occurring. TRAPPIST-1e, f, and g, however, represent the holy grail for planet-hunting astronomers, as they orbit in the star's habitable zone.

These new discoveries make the TRAPPIST-1 system a very important target for future study. The NASA/ESA Hubble Space Telescope is already being used to search for atmospheres around the planets and team member Emmanuël Jehin is excited about the future possibilities: "With the upcoming generation of telescopes, such as ESO's European Extremely Large Telescope and the NASA/ESA/CSA James Webb Space Telescope , we will soon be able to search for water and perhaps even evidence of life on these worlds."

This research was presented in a paper entitled "Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1", by M. Gillon et al., to appear in the journal Nature.

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"some of these zones might not actually be able to support life due to frequent stellar eruptions – which spew huge amounts of stellar material and radiation out into space – from young red dwarf stars."

There is also the issue that we have no idea what conditions are required for biogenesis. Just because life can live somewhere doesn't mean it come into being through biogenesis there. They may be great locations for future human colonies though For instance light from red dwarves is very different from light from our sun. Light from red dwarves is concentrated on forms of light with lower energy. This makes a big difference to the chemical reactions that could occur on the planet. Red dwarves may lack sufficient high energy rays for vital life chemical reactions to occur. In addition, before DNA evolved the spectral content of the star could be a big factor for controlling what chemical reactions are taking place. Review the rare earth solution to the Fermi paradox

The various dangers of being close to a red dwarf in other articles include that the star can have significant solar flares (necessitating a more powerful, and thus less likely, planetary magnetic field to prevent sharp atmospheric loss over time), a higher intensity of X-ray bombardment in the liquid water distance zone, and the likelihood of a close in planet being tidally locked, and this is not necessarily an exhaustive list. If anything, one gets the impression these are much less likely places to find life as we know it than a system more similar to our own.

Amazing to think an entire solar system with so many earth size planets that's just a little bigger than the size of Jupiter and it's moon's orbits. I wonder if the planets experience gravity tidal perturbations as other planets come in close to each other. Glad we finally found our future home system, ultra cool dwarf stars last forever.

Sounds like a good opportunity to detect intelligent live: Just look for gamma rays originated from nuclear explosions. Having 7 planets so close to each other... if there is live and they are like us then they could be at war very often.

Re: "The various dangers of being close to a red dwarf in other articles include that the star can have significant solar flares ... If anything, one gets the impression these are much less likely places to find life as we know it than a system more similar to our own."

The fact that they can have significant flares would probably only imply discontinuities in evolution. Whether or not life is supported would depend more on the conditions, I would imagine ...

Are we really any different than a colony of bacteria in a petri dish discovering other habitable petri dishes on the other side of the lab? Of course, the distance between our dish we call home and the far one would seem insurmountable, but this is just the beginning of our efforts to bridge the gap. We owe it to our slimy selves to colonize any place that we can survive, it's hardwired in us. We may not be the ones who get there, but take solace that our corpses will be the bricks in the bridge for our descendants to cross.

The fact that they can have significant flares would probably only imply discontinuities in evolution. Whether or not life is supported would depend more on the conditions, I would imagine ...

Huh? Flares every few weeks, or months, would cause more than just 'discontinuities'! That isn't to say life couldn't exist underground, or in any putative oceans. However, these flare stars are liable to strip a planet of its atmosphere, and therefore its water.

This system has the potential to cause problems for the planetary sciences for the very reason that it is somewhat similar to our own.....

How, exactly? Everything looks normal re their orbital resonances etc. And the whole system would fit well inside the orbit of Mercury. No gas giants or ice giants, either. Not exactly too similar to our own.

Although super flares are more common on red dwarves, this does not mean every red dwarf has super flares. Our star, for example, is much more calm than similar stars. We cannot just assume the red dwarf in this star has frequent super flares etc.

At a distance of 40 light years, the possibility of any of these planets becoming "our future home system" is about as likely as me growing wings and flying there in a week. The speed of light is 300,000 kilometres per second; the fastest human spacecraft flight to date is 17 kilometres per second, or 1/17,647th the speed of light. Lacking a fictional Star Trek warp drive, or a massive Project Orion spacecraft propelled by the sequential explosion of hundreds of nuclear devices (!), that is going to be one heck of a lo-o-o-o-o-ng journey - i.e. hundreds of thousands of years - with no certainty that any of those 7 planets can actually support human life.

If our current technology curve continues we will have the technology for a trip like this within a hundred years. But, even if we had the technology for the trip, we still need to know where to go and what to expect. Articles like this are great because it gives us a better idea of what is out there and as better telescopes etc. Are deployed into space we will learn more about systems like this and hopefully determine their hospitality.

"Assuming a perfect anti-matter drive (exhaust is light-speed and all in the right direction), then the mass fraction for the 1g trip is 39.5. That is, for every kilo of payload delivered to Alpha Centuri, you would need 38.5 kilos of fuel (half matter and half antimatter)"http://forum.nasa...=34996.0

-So 1g might be a little unrealistic.

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